Simple and quick tip for WordPress. You might run into this if you have code snippets or other things in the HTML view that get malformed once you enter the visual view of the editor.

This WP plugin covers the basic functionality. The minor issue is that you have to open the post’s edit view to input the custom field, instead of having a button in the list of posts section of the admin area. Maybe there is a plugin for editing custom fields ajax-style, or a richer version of this visual/html toggle that I may have missed.